Sahih Bukhari | Volume 6 | Hadith Number 535

Narrated by 'Aisha
Whenever Allah's Apostle became sick, he would recite Mu'awwidhat (Surat Al-Falaq and Surat An-Nas) and then blow his breath over his body. When he became seriously ill, I used to recite (these two Suras) and rub his hands over his body hoping for its blessings.